The present invention relates generally to mechanisms for extending and retracting crane booms and the like, and particularly to mechanisms that extend and retract sequentially. More particularly, the invention relates to sequentially extending and retracting mechanisms utilizing integral control means to control the sequencing of the extension and retraction.
Crane booms and the like are useful devices for lifting and moving loads of various types and allowing access to areas that might otherwise be out of reach. For instance, crane booms make it easier for utility workers to reach the top of utility poles and allow tree trimers to reach the tops of trees, especially where the limbs might not be strong enough to support a person's weight.
It is advantageous to provide the crane booms and the like with extensible and retractable boom sections that telescope within each other in the retracted position. It has been customary to attach a hydraulic cylinder to one section and connect a piston actuated by the cylinder to an adjacent section so that actuation of the hydraulic cylinder provides relative motion between the sections.
Piston and cylinder assemblies for extending and retracting crane booms and the like are known. See, for example, U.S. Pat. No. 3,841,494 to Chalupsky et al.; U.S. Pat. No. 3,633,460 to Ohniwa et al.; U.S. Pat. No. 3,657,969 to Wirkus; U.S. Pat. No. 2,787,383 to Antos et al.; U.S. Pat. No. 3,610,433 to Milner, Jr. et al.; U.S. Pat. No. 3,300,060 to Lado; U.S. Pat. No. 3,250,182 to Nansel; U.S. Pat. No. 3,481,489 to Stauffer; U.S. Pat. No. 4,775,029 to MacDonald et al.; Russian Patent Document No. SU 1138-381; and German Patent Document No. 2 310 550.
Generally, crane booms utilize long hydraulic fluid supply lines that extend the length of the crane boom to supply pressure for actuating the cylinders mounted in the extended sections. Typically, take up reels are necessary to keep the supply lines from becoming entangled or interfering with the extension and retraction of the telescoping sections. Moreover, typical crane booms and the like use mechanical latches alone or in combination with hydraulic valves to sequence the extension and retraction in a predetermined order.
An extension and retraction mechanism that eliminates the long supply lines and take up reels as well as the mechanical latches would be a tremendous improvement over conventional extension and retraction mechanisms. Such a mechanism would be more reliable and maintainable by eliminating equipment that is otherwise subject to failure.
According to the present invention, a mechanism for extending and retracting a telescoping unit includes a plurality of interconnected power cylinders that are movable between an extended and a retracted position. Each cylinder includes an extension passage, a retraction passage, and a flow-through passage. Moreover, each cylinder has hydraulic holding mechanisms for preventing the unintentional movement of the cylinders and sequencers to initiate retraction of the cylinders in sequence, retraction beginning with the last cylinder and extension beginning with the first cylinder.
According to one aspect of the invention, the sequencers include a position sensitive mechanism for blocking fluid flow from traveling from the retracting cylinder to the next cylinder in the retraction sequence until the retracting cylinder is fully retracted. In a preferred embodiment, the sequencer is a poppet control check valve.
According to another aspect of the invention, the holding mechanism is formed to be integral with the power cylinder and includes a one-way check valve and a retraction pressure signal input, and provides a hydraulic lock.
In another preferred embodiment, a mechanism for extending and retracting a telescoping unit includes cylinders formed to include an external wall and a piston having a plurality of passages for transmitting a pressure signal, and load-holding mechanisms for preventing the unintentional retraction of the mechanism under the action of a load. It further includes first valves for controlling the transmission of the pressure signal so that the mechanism extends sequentially in order, and valves for controlling the transmission of the pressure signal so that the mechanism retracts sequentially in reverse order. Moreover, the valves and the load holding mechanism are formed to be integral to the cylinder means.
According to another aspect of the invention, each cylinder is formed to include an extension pressure inlet port, and first and second apertures formed in the external wall. Each piston includes a first passage fluidly connecting the extension pressure inlet port to the first aperture and a second passage fluidly connecting the second aperture to the extension passage in the piston rod. A by-pass boss is formed on the external wall to fluidly connect the first and second apertures, thereby providing fluid communication between the extension pressure inlet port and the extension passage in the piston rod.
According to yet another preferred embodiment, an extension and retraction mechanism comprises a fluid motor including first, second, and third inlet ports and first, second, and third outlet ports. The mechanism also has first mode for activating the fluid motor in a first direction by connecting the first inlet port to the first outlet port. It further includes a passage for circumventing activation of the fluid motor by connecting the second inlet port to the second outlet port, and a second mode for activating the fluid motor in a second direction by connecting the third inlet port to the third outlet port.
Advantageously, the use of three separate passages in the piston and cylinder, the extension passage, the flow-through passage, and the retraction passage, allows hydraulic fluid to flow-through the system internally and eliminates the need for a take-up reel and long supply hoses which could become entangled or interfere with the operation of the system. Moreover, the hoses that are used to interconnect the cylinders of the present invention are short, fixed in position, and are not required to flex. This simplifies the design and eliminates accessory equipment that requires maintenance and is subject to failure.
description of a preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.